FH3 is a given...guess again
There is no need for Project Gotham Racing since we have Horizon, so can't be that...
Open world Kart racer like Forza Horizon with Karts? LOL. Could be cool if it has a Splatoon like aesthetic.
Yeah. Imagine all the themed zones they could cram into a space like FH2. It wouldn't have to be a realistic setting, so they could go nuts.
Also have things from Sonic Racing Transformed like air/land/sea capabilities plus mods.
Shared world, too.
What does (design) and (build) entail?
Like they did with Forza Horizon 2. I assume Playground designed the whole game and Sumo built the 360 version.
Given how great the Sonic Racing games turned out I'd trust Sumo with some design, but Playground has proven they have skill when it comes to designing for open world.